The present disclosure relates to Positron Emission Tomography (PET) data acquisition, more particularly to tracking loss of coincident event packets in real time.
Nuclear medicine is a unique medical specialty wherein radiation is used to acquire images which show the function and anatomy of organs, bones or tissues of the body. Radiopharmaceuticals are introduced into the body, either by injection or ingestion, and are attracted to specific organs, bones or tissues of interest. Such radiopharmaceuticals produce gamma photon emissions which emanate from the body and are captured by a scintillation crystal, with which the photons interact to produce flashes of light or “events.” Events are detected by an array of photodetectors, such as photomultiplier tubes, and their spatial locations or positions are calculated and stored. In this way, an image of the organ or tissue under study is created from detection of the distribution of the radioisotopes in the body.
One particular nuclear medicine imaging technique is known as Positron Emission Tomography, or PET. PET is used to produce images for diagnosing the biochemistry or physiology of a specific organ, tumor or other metabolically active site. Measurement of the tissue concentration of a positron emitting radionuclide is based on coincidence detection of the two gamma photons arising from positron annihilation. When a positron is annihilated by an electron, two 511 keV gamma photons are simultaneously produced and travel in approximately opposite directions. Gamma photons produced by an annihilation event can be detected by a pair of oppositely disposed radiation detectors capable of producing a signal in response to the interaction of the gamma photons with a scintillation crystal. Annihilation events are typically identified by a time coincidence between the detection of the two 511 keV gamma photons in the two oppositely disposed detectors, i.e., the gamma photon emissions are detected virtually simultaneously by each detector. When two oppositely disposed gamma photons each strike an oppositely disposed detector to produce a time coincidence event, they also identify a line of response, or LOR, along which the annihilation event has occurred.
When the rate of PET coincidence detection exceeds the receiving rate provided by the PET data handling system, PET patient data are lost. Ideally, PET data collection systems of sufficiently high bandwidth are made available to avoid such loss. However, the size of the PET detector array is ever expanding as the state of the art progresses. Optical matching of maximum possible data collection rates to that of maximum possible data generation rates is not always possible.
If the actual generated PET coincidence event data cannot be stored and/or processed as generated, precisely tracking the loss of such data can preserve the accuracy of PET quantitation. Techniques are thus needed for keeping precise track of loss of PET coincidence data in real time.